The processes of non-catalytically cracking and catalytically cracking hydrocarbon feedstocks are well known in the art. In this regard, steam cracking in a furnace and contact with hot non-catalytic particulate solids are two well known non-catalytic cracking processes, as described, for example in Hallee et al., U.S. Pat. No. 3,407,789; Woebcke, U.S. Pat. No. 3,820,955, DiNicolantonio, U.S. Pat. No. 4,499,055 and Gartside et al., U.S. Pat. No. 4,814,067. Additionally, fluid catalytic cracking and deep catalytic cracking are two well known catalytic cracking processes. See, e.g., Cormier, Jr. et al., U.S. Pat. No. 4,828,679; Rabo et al., U.S. Pat. No. 3,647,682; Rosinski et al., U.S. Pat. No. 3,758,403; Gartside et al., U.S. Pat. No. 4,814,067; Li et al., U.S. Pat. No. 4,980,053; and Yongqing et al., U.S. Pat. No. 5,326,465.
The olefins produced in these processes have long been desired as feedstocks for the petrochemical industries. Olefins such as ethylene, propylene, the butenes and the pentenes are useful in preparing a wide variety of end products, including but not limited to polyethylenes, polypropylenes, polyisobutylene and other polymers, alcohols, vinyl chloride monomer, acrylo-nitrile, methyl tertiary butyl ether and tertiary amyl methyl ether and other petrochemicals, and a variety of rubbers such as butyl rubber.
However, there has been little incentive in the industry to integrate the cracking processes which produce the olefins with the olefin derivative processes which produce the end products due to either the inability of the respective processes to handle dilute olefin feeds, the difficulty in recycling the by-products produced in the respective processes or both as well as logistical reasons.
For example, in the polymerization processes to produce polyethylene and polypropylene, historically the location and infrastructure associated with ethylene-polyolefin units has made integration a difficult logistics problem. More importantly, recycle streams from the polyolefins units have until recently contained corrosive products from the catalyst deactivation reactions and other impurities.
Additionally, the feedstocks conventionally required for the production of polyethylenes and polypropylenes have demanded that methane, ethane and propane concentrations in the ethylene and propylene feedstocks be extremely low. For example, for ethylene, the minimum concentration of ethylene is typically about 99.9 mol % and for propylene the minimum propylene concentration for polymer grade propylene is typically about 99.0 mol %.
These ethylene and propylene feedstock specifications have required extensive and costly purification in the olefin recovery section of the cracking processes. Typically, the ethylene concentration in the C.sub.2 stream from a cracker gas separation system ranges from about 55 to about 85 percent. The higher purity ethylene stream conventionally requires additional separation in a C.sub.2 splitter.
Still further, advancements in polymerization catalysis, with the introduction of the "single site" metallocene catalysts, have resulted in even more stringent feedstock purity requirements due to the expanding usage of these high activity catalysts. See, e.g., Chang, U.S. Pat. No. 5,238,892; Burkhardt et al., PCT Application No. WO 9212184; and Schreck et al., U.S. Pat. No. 5,280,074.
Accordingly, the conventional wisdom in the industry is for olefin derivative producers, including, polyethylene and polypropylene producers, to purchase polymer grade ethylene and propylene from ethylene and propylene producers and then remove trace contaminants to the desired purity specifications and recover, flare or utilize the purge streams from the olefin derivative reactor within the processing plant.
Traditionally, ethylene and propylene unit operators have not accepted the recycle streams from the olefin derivative units because they typically contain undesirable light gases and inorganic acids resulting from catalyst deactivation reactions.
However, with ethylene and propylene units now being built in more remote and unsophisticated locations close to feedstock supply sources, it has now become desirable to develop a single integrated process which will produce the desired olefin derivative products as the final output of the integrated plant.
Additionally, existing refineries have long experienced problems of gas plant bottlenecking when increasing the capacity or conversion level of their various cracking units. The inability to market the relatively dilute olefins produced in the refinery to downstream purification processors has further compounded the problem. Thus, it has also become desirable to develop a means of revamping an existing refinery to debottleneck the gas plant and market the dilute olefins produced therein.
Accordingly, if such a means to integrate cracking with olefins derivative processes were to be developed it would represent a significant advancement in the state of the art including the realization of significant capital and operating cost savings for end product producers.